When looking at ancient armor, for example the Greek helmets, wouldn't it have burned to wear this in an environment that was both sunny and extraordinarily hot in the summer? The suits of armor in the medieval ages seems like it would have been ridiculously hot as well, and would make it difficult to perform in combat with that amount of heat stress.
Was the armor padded on the inside and if so, was heat stroke fairly common in battle? Even today heat stroke is a legitimate concern with our troops in the Middle East, I'm just curious how militaries in centuries past dealt with this issue, and why they weren't burned by their metal armor in the sun.
You are asking about thousands of different years and numerous permutations of technology so I'll just answer your first example, the Greeks.
The greek hoplite often had long hair. The Spartans for example were very proud of their locks and before battle would bathe them in oil and make sure they were clean and well arranged. Ritual aside (it probably has some religious significance as well I don't know about) This also served the purpose as extra insulation from blunt force trauma.
Also many helmets such as the chalcidian style were often given leathe rlinings on the inside or the citizen would wear a cap of some sort of material. Finally when not in battle the preferred resting method for many of the popular helmet styles you see in greek art and what archaeologists find such as the Corinthian and Phyrgian style was to have the helm pulled up and resting on the crown of the head. Look at art form the period especially statues and this is very clear. This wasn't an artistic license taken they actually had the helmet like that when they were not in battle.
Like this. Interesting tidbit. If the statue has the helm pulled down the artist was trying to represent something radically different than if the helm was up. It wasn't a random spur of the moment choice.
http://downloads.bbc.co.uk/rmhttp/schools/primaryhistory/images/ancient_greeks/athens/g_perikles.jpg
The same sort of things applied to any helmet you can think of. Medieval armor had tons of padding in the manner of coifs (both chain and additional cloth and quilt layers), gambesons, etc. Usually the heavy metal helms would not go until battle was assured.
Well, as centurion44 mentioned you very seldom wore metal directly against the skin, but more importantly is that if you did you still would not get burned!
The reason for this is quiet simple: metal is a great conductor of heat and while this means that heated metal will burn you it also means that it will very quickly transfer away it's heat when it's not being heated quicker than it can cool. When in contact with your skin, metal will transfer it's heat to you (because you are a better conductor than the sounding air), and will pretty pretty quickly find a point of equilibrium, where your skin transfers the heat away as quickly as the sun can add it. At this point the metal will only be sort of warm. And you only need to step in to a shadow for this to very quickly start cooling instead of heating you.
Tl;dr: You will get warm, but you won't get burned. The armor will transfer it's heat to you and the air.
